Chemistry Reference
In-Depth Information
Table 9.1
Data for factor
k
1
in Equation 9.2 as a
function of electrode surface area (
A
) for a constant
distance between the electrodes of
d
=
112 mm
Electrode surface area (mm
2
)
k
1
19.63
136.0
78.50
53.0
176.60
30.5
314.00
20.6
490.60
15.3
where
k
2
is a factor containing the unknown parameters and relationships
and
- .
068
kkA
1
=◊
[9.4]
2
From the data in Fig. 9.6, it is possible to calculate the value of
k
1
for various
electrode surface areas as was done in the previous section for a surface
area of 314 mm
2
. In addition, with the knowledge of these values, it is pos-
sible to obtain the value of
k
2
using Equation 9.4. The values for
k
1
are sum-
marised in Table 9.1, while for
k
2
a value of 1030 ± 40 was obtained, with
A
in mm
2
. It can be seen that the value for
k
1
at
A
= 314 mm
2
is in acceptable
correlation with the value obtained in the previous section.
9.2.5
Study of the influence of the distance between
the electrodes
In this section, the influence of the distance between the electrodes is inves-
tigated as a function of NaCl concentration (1 ¥ 10
-1
-1 ¥ 10
-4
mol l
-1
) and as
a function of electrode surface area (19.6-490.6 mm
2
). The distance between
the electrodes was varied from 27 to 112 mm by inserting PVC pipes of dif-
ferent lengths into the cell. Additionally in this case, the impedance of the
cell was measured as a function of applied frequency, and the impedance
of importance for this work is the one at the completion of the semi-circle
in Fig. 9.8 (or values corresponding to the observation of no phase-angle
shift between applied potential and measured current). As an example of
these experiments, Fig. 9.7 shows the logarithmic plot of the relationship
between obtained impedance and distance between the electrodes for the
four different concentrations of electrolyte and at a fixed value for the elec-
trode surface area (490.6 mm
2
).
It can be seen that linear relationships are obtained with a slope very
close to 1, indicating that the impedance is proportional to the distance
